Nematodes are inoculated in plants to evaluate plant-nematode relationships and to establish nematode association, nematode involvement, or the role of the nematode in the disease development. Inoculation varies depending on the experimental purpose it will serve.

The first stage in studying plant-nematode relationships is a strong evidence of the suspected nematode involvement in the disease. Observing nematodes feeding or on in the host is useful at association stage and this can be done through general field observations, nematode surveys, soil fumigation studies and preliminary greenhouse inoculation experiments.

The second stage is to establish that the nematode is involved in the disease development. This is achieved by conducting inoculation experiments under controlled conditions. Observations and experiments may involve other microorganisms other than the nematodes which is the reason why graded series of nematode inocula may be added to the non-infested soil to establish a treated and non-treated check for comparison and correlation of the differences due to nematode population.

Experiments should be done under asceptic condition to establish the role of the nematodes in the disease or its activity in the plant. A microbiologically sterile single population of nematode should be used.

For the purpose of this experiment, Meloidogyne incognita, a root-knot nematode, is used to determine if it is responsible for the development of root-knots in Lycopersicum esculentum (tomato).

Methodology

A gram of infected roots were placed near the base of a set of tomato plants. Another set were prepared this time placing 20 grams of infested soil. The plants were arranged in the greenhouse following a randomized block manner. Initial plant heights were gathered and data were collected every week for four weeks. After four weeks, the final heights of the tomato plants were recorded. The tomato plants were removed from the pots carefully so as not to leave any plant roots on the soil. Afterwhich, the roots were washed to remove excess soil particles followed by the counting of the root-knot formations on the roots. The data were recorded.

Results and Discussion

The initial and final plant heights were recorded and the height differences were calculated.  Galls were also counted and were evaluated using the following index:  (RGI-Root Galling Index*) 1 – no gall, 2 – trace galling (1-25% galling), 3 – slight galling (26-50%), 4 – moderate galling (51-75%) and 5 – severe (76-100%).

Height differences were calculated so as to have a simple basis of comparison for the effects of the root-knot formation caused by Meloidogyne incognita on Lycopersicum esculemtum while the counting of the number of nematodes can be used for analyzing how the nematode population can affect the growth of the plant.

Below are the data gathered during the experiment:

Table 1. Data gathered for Lycopersicum esculentum with no inoculation to serve as control

Table 2. Data gathered for Lycopersicum esculentum inoculated with Meloidogyne incognita using an infested soil as source of inoculum.

Table 3. Data gathered for Lycopersicum esculentum inoculated with Meloidogyne incognita using galled roots as source of inoculum.

Table 4. Average height differences, number of galls and index of the three treatments.

Data has shown us that of number of galls is highest on plants whose source of inoculum was the galled tomato roots giving it a moderate galling (4) in the RGI while the control treatment showed no signs of galling, hence an index value of 1. The average growth of the plants has negligible differences so we look at the number of galls that were formed from t plants respectively and it can be noted that many galls were formed especially in the plants inoculated with nematodes from galled tomato roots. Hence, more nematodes came from the galled tomato roots. This means that between the two sources of inoculum, the use of galled tomato roots will yield more disease formation. It can also be noted that since the same galls from the inoculum were formed in the test plants, it can be concluded that the same nematodes were the cause of both the diseases observed.

Conclusion

Since the same gall formation were observed from the source of the inoculum and the test plants, it is confirmed that the presence of the nematode is indeed the cause of the disease since no galls were observed from the control set-up and galls were also observed from the roots of test plants inoculated with infested soil.